Synovial osteochondromatosis presenting as a mass in the buttock

A 42-year-old woman, who had received a radiologic diagnosis of synovial os teochondromatosis many years before, was examined for a painful right hip a nd a large immobile mass in the right buttock. Findings of radiologic and s cintigraphic imaging were consistent with synovial osteochondromatosis. The patient underwent arthrotomy and excision of the large mass and several sm aller masses to control pain and to identify possible malignant change.